My CEL came on again and I had it checked out. I'm getting code 0420, Catalyst System Efficiency below Limit - Bank No 1, but the mechanic said it is most likely being caused from the downstream O2 sensor.
They did a test with the engine running and found that there was no signal coming from Bank 1 sensor 2. The mechanic said this is strange because usually the sensor will just be out of spec. He said it would be rare for the sensor to fail in this way (no signal) and that more likely it was a problem with the O2 sensor wiring.
What do you guys think? Or is it really the cat?
2002 BMW M5
Carbon Black on Black
1998 Frost Silver SVT E0
17" Masitaly rims with Bridgestone Fuzion ZRi rubber.
133,000km
1996 Silver Ford Taurus SHO ATX
180,000km - SOLD!
1996 Midnight Red SE MTX
295,000km and a little squeeky.
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